The present invention relates to the removal of dissolved oxygen from fuels, and more particularly to acoustic induced flow mixing and gas cavitation.
Hydrocarbon jet fuel significantly increases its heat capacity if it is heated up. The presence of dissolved oxygen in jet fuels may be objectionable because it supports oxidation reactions that yield undesirable by-products. Dissolution of air in jet fuel results in an approximately 70 ppm oxygen concentration. When aerated fuel is heated between 350° F. and 850° F. the oxygen initiates free radical reactions of the fuel resulting in deposits commonly referred to as “coke” or “coking.” Coke may be detrimental to the fuel lines and may inhibit combustion. The formation of such deposits may impair the normal functioning of a fuel delivery system, either with respect to an intended heat exchange function or the efficient injection of fuel.
Typically, lowering the oxygen concentration to approximately 2 ppm is sufficient to overcome the coking problem. Various conventional fuel deoxygenation techniques are currently utilized. One conventional Fuel Stabilization Unit (FSU) utilized in the aircraft field removes oxygen from jet fuel by inducing an oxygen pressure gradient across a membrane permeable to oxygen. Although quite effective, the rate of degassing is proportional to the gas concentration at the sub surface membrane layer, which is determined by the diffusion rate of the solute from surrounding fluid.
Various flow mixing systems, typically utilizing a geometrically arranged groove and baffle structure, more effectively provides the gas to the depleted boundary regions. Other turbulent mixing systems include dynamic structures such as impellers located within the fuel flow. However, turbulent mixing may not always be feasible or energetically beneficial as a fully developed turbulent flow may result in an unacceptably high pressure drop in applications that require relatively long fuel channels as typified in an aircraft. Furthermore, geometrically forced mixing structures are relatively difficult to manufacture and may become fouled over a prolonged time.
Accordingly, it is desirable to provide a method and system for the deoxygenation of hydrocarbon fuel, which minimizes coking in an inexpensive, size and weight efficient system which avoids the utilization of geometrically forced mixing structures.